I am creating a plugin to support a new language, and I want to add "Goto definition" functionality, but I am not sure where to start with this. Are there any other language plugins that support this kind of thing? Is Sublime even suited for this? Anything would help me at this point.

A few plugins have this functionality. For example, SublimeCodeIntel, SublimeRope, and SublimeClang have "go to definition." What nick. is referring to is the "Go To Symbol" panel which displays a list of all the methods in the current file. You can get to this panel by pressing @ in the Go To Anything panel (control+p). This also works for any file in the current project. filename#function_name. I'm assuming you're referring to highlighting a method and pressing some keystroke to take you the the declaration of said function.